1. Field of the Invention
The present invention relates to encapsulated Gyricon spheres that are not required to be embedded in an oil-filled elastomer binder sheet, to novel displays employing such encapsulated spheres, and to methods of making such encapsulated spheres and displays.
2. Discussion of Related Art
Gyricon displays, also called twisting-ball displays, rotary ball displays, particle displays, dipolar particle light valves, reimageable displays, etc., offer a technology for making a form of electric paper. Briefly, a Gyricon display is an addressable display made up of a multiplicity of optically anisotropic balls, each located within a fluid-filled cavity of a transparent sheet such as an elastomer, and each of which can be selectively rotated to present a desired face to an observer. For example, a Gyricon display can incorporate balls each having two distinct hemispheres, one black and the other white, with each hemisphere having a distinct electrical characteristic (e.g., zeta potential with respect to a dielectric fluid) so that the balls are electrically as well as optically anisotropic. The black-and-white balls are embedded in a sheet of optically transparent material, such as an elastomer layer, that contains a multiplicity of spheroidal cavities and is permeated by a transparent dielectric fluid, such as a plasticizer. The fluid-filled cavities accommodate the balls, one ball per cavity, so as to prevent the balls from migrating within the sheet. A ball can be selectively rotated within its respective fluid-filled cavity, for example by application of an electric field, so as to present either the black or the white hemisphere to an observer viewing the surface of the sheet. Thus, by application of an electric field addressable in two dimensions (as by a matrix addressing scheme), the Gyricon balls or spheres rotate in response thereto, thereby presenting either a black or white side surface to the viewer.
Preparation of these known types of Gyricon displays involve several steps. First, the Gyricon spheres must be cast in the transparent sheet material, for example a silicon elastomer sheet. The sheet is then cured and immersed in a dielectric fluid such as oil. The sheet absorbs the oil, and oil-filled pockets form around each Gyricon sphere.
An exemplary Gyricon display 10 of this type is shown in side view in FIG. 1. Bichromal balls 11 are disposed in an elastomer binder of the sheet 12 that is swelled by a dielectric fluid creating cavities 13 in which the balls 11 are free to rotate. The balls 11 are electrically dipolar in the presence of the fluid and so are subject to rotation upon application of an electric field, as by matrix-addressable electrodes 14a, 14b. The electrode 14a closest to viewing surface 15 is preferably transparent. An observer at I sees an image formed by the black and white pattern of the balls 11 as rotated to expose their black or white faces (hemispheres) to the viewing surface 15 of sheet 12.
U.S. Pat. No. 5,389,945, incorporated by reference herein, shows that Gyricon displays can be made that have many of the desirable qualities of paper, such as flexibility and stable retention of a displayed image in the absence of power, not found in CRTs, LCDs, or other conventional display media. Gyricon displays can also be made that are not paper-like, for example, in the form of rigid display screens for flat-panel displays.
Typically, known Gyricon displays are made up of bichromal balls that are black on one hemisphere and white on the other. Other kinds of rotating elements are also known. For example, U.S. Pat. No. 4,261,653 shows a multilayer sphere, although it is made at least in part from glass and its use depends on an addressing scheme involving high-frequency electric fields.
Other commonly owned patents related to Gyricon displays, each incorporated herein by reference in their entireties, include U.S. Pat. Nos. 5,262,098, 5,344,594, 5,717,514, 5,815, 5,989,629 and 6,097,531.
There are several drawbacks to existing Gyricon display technology. The Gyricon elastomer sheet must be kept wet with oil in order for the balls to maintain their rotation capabilities, as evaporation of the oil from the sheet (such as would occur upon exposure to the atmosphere) causes collapse of the cells and immobilization of the Gyricon spheres therein. Also, the need to have the spheres embedded within sheets, as well as the need to limit exposure to the atmosphere, severely limits the ease of use of the display.
What is still needed is an improved Gyricon display and method of making the same that permits more practical displays to be made.
It is therefore an object of the present invention to develop a method of making novel Gyricon spheres that are not required to be embedded in a sheet, and thus does not require constant exposure to the dielectric fluid to maintain the cavities within the sheet.
It is a further object of the present invention to develop a method of making the novel Gyricon sphere that is efficient and cost effective.
It is a still further object of the present invention to develop novel Gyricon displays that have greater ease of manufacture and use, thereby increasing the utility of the technology.
These and other objects of the present invention are achieved herein by obtaining self-contained particulate encapsulated Gyricon elements, each comprised of a Gyricon sphere encapsulated within a shell that also contains a dielectric fluid in which the Gyricon sphere is able to rotate.
These and other objects are also achieved by a method of making an encapsulated Gyricon element comprised of an encapsulating shell containing a Gyricon sphere and a dielectric liquid, comprising encapsulating the Gyricon sphere and the dielectric liquid with the encapsulating shell by forming the shell by interfacial condensation polymerization in the presence of the Gyricon sphere and the dielectric liquid.
These and other objects are also achieved by a display element, comprising one or more particulate encapsulated Gyricon elements upon a substrate, wherein the particulate encapsulated Gyricon elements comprise a Gyricon sphere encapsulated within a shell that also contains a dielectric fluid in which the Gyricon sphere is able to rotate.
These and other objects are further achieved by simple, convenient method of making the display elements, comprising applying to a substrate one or more encapsulated Gyricon elements comprised of a Gyricon sphere encapsulated within a shell that also contains a dielectric fluid in which the Gyricon sphere is able to rotate.
By self-containing the Gyricon spheres within dielectric fluid filled encapsulated shells, display elements can be easily made without the need for an expensive elastomer binder sheet or the need to have the sheet in contact with a dielectric fluid.